The present invention relates to an apparatus for supplying a chemical solution to a manufacturing apparatus of an electronic device, such as a semiconductor device and an LCD device. More particularly, the present invention relates to an apparatus for supplying a mixed chemical solution having a predetermined concentration prepared by mixing a plurality of stock chemical solutions.
In a manufacturing process of electronic devices, many kinds of chemical solutions are used in large quantities. Specifically, a diluted chemical solution and/or a mixed chemical solution prepared by mixing a plurality of stock chemical solutions at predetermined concentrations are used in large quantities.
The mixed chemical solution is prepared by a chemical solution supply apparatus. The chemical solution supply apparatus has a conductivity meter for measuring the electrical conductivity, a sonic speedometer for measuring sonic velocity (propagation velocity of a sonic wave in the chemical solution), and a thermometer for measuring temperature of the chemical solution. The chemical solution supply apparatus measures the concentration of the mixed chemical solution by comparing the measured values of the electrical conductivity, the sonic velocity and the temperature with the calibration curves prepared beforehand. The chemical solution supply apparatus adjusts the mixture ratio of a plurality of stock chemical solutions so that the measured concentration may be equal to a predetermined value, and supplies the mixed chemical solution maintained at the predetermined concentration to a device manufacturing apparatus.
Furthermore, a mixed chemical solution regulated to the predetermined concentration beforehand may be purchased from a chemical solution maker, and may be supplied to the device manufacturing apparatus.
However, when the chemical solution supply apparatus stirs a mixed chemical solution, bubbles are generated in the mixed chemical solution, and the bubbles adhere to the conductivity meter, the sonic speedometer and the thermometer. The measured values vary owing to the stuck bubbles, so that the electrical conductivity, the sonic velocity and the temperature cannot accurately be measured, which makes it difficult to maintain the concentration of the mixed chemical solution at the desired concentration. As a result, the concentration of the mixed chemical solution supplied to the device manufacturing apparatus varies, so that defects easily occur in semiconductor devices manufactured by the device manufacturing apparatus.
In order to accurately measure the concentration of a mixed chemical solution, it has been suggested that an automatic neutralization titration apparatus in which neutralization titration is automatically carried out be incorporated into the chemical solution supply apparatus. However, since the neutralization titration analysis takes about ten minutes at the shortest for one analytical operation, even the automatic neutralization titration apparatus cannot monitor the concentration of a mixed chemical solution throughout.
Furthermore, it is necessary to replenish the reagents required for the neutralization titration analysis, and the shorter is the interval between the neutralization titration analysis operations, the shorter is the replenishment interval of the reagents. In consequence, the replenishment operation becomes complicated. In addition, a drainage treatment for purifying the waste liquid generated by the neutralization titration analysis is also required.
On the other hand, when a mixed chemical solution adjusted to the predetermined concentration is purchased from a chemical solution maker, a unit price of the chemical solution is higher than that of a single component chemical solution. Moreover, the time period between the manufacture of the chemical solution by the chemical solution maker and the supply of the chemical solution to the device manufacturing apparatus is long, and hence, it is difficult to maintain the concentration of the mixed chemical solution.